Motorola PowerQUICC II MPC8280 Series Reference Manual page 1214

IMA Protocol Overview
facilitates HEC checking of received cells. (Refer to Chapter 35, "ATM Transmission
Convergence Layer.") So in these MPC8280 devices, IMA support is available for either
the integrated DS1/E1 TC layer or external UTOPIA PHY devices connected via UTOPIA
Level 2 multi-PHY.
34.1.4 PHY-Layer Devices Supported
The IMA microcode is primarily targeted at ATM's primary application (i.e. IMA over
multiple DS1/E1). However, the IMA microcode supports any UTOPIA PHY device which
(1) has a constant data rate and (2) can be programmed not to screen out HEC-errorred cells.
Most PHYs have this mode available for IMA also.
34.1.5 ATM Features Not Supported
The following ATM features are not available for IMA links only, but are available for
non-IMA links:
• User-defined cells (UDC) (i.e. cells that are not 53 bytes and/or with customized
headers)
• Internal rate mode for APC scheduling
34.1.6 Additional Impact on MPC8280 Features
If the IDCR recovery feature is used, the following are true:
• One of the IDMA channels are unavailable, and its resources are dedicated instead
to the IDCR master clock function. This can be any IDMA channel (1, 2, 3, or 4).
• MPC8280 features sharing the IDMA channel's parameter RAM page are
unavailable.
For more detailed information, refer to Section 34.4.8.2, "IDCR FCC Parameter Shadow."
34.2 IMA Protocol Overview
This section describes the IMA protocol, not the MPC8280's IMA microcode.
34.2.1 Introduction
Inverse Multiplexing over ATM (IMA) provides a cost effective solution to carry high
speed connections, for example, T3/E3 and OC-3c/STM-1 links, over already installed low
speed connections, for example, T1/E1 links, in a flexible way by dynamically
adding/removing links as required, depending on the bandwidth required.
IMA is defined as transmitting a stream of data over multiple low speed links and
recombining the stream in the correct order at the end. IMA involves inverse multiplexing
34-4
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